1. Field of the Invention
The present invention relates to a deflection yoke for use with a color CRT having an in-line type electron gun.
2. Description of the Related Art
A deflection yoke is mounted on a neck of a color CRT in which three electron guns are incorporated. The deflection yoke is energized to magnetically deflect three electron beams both horizontally and then vertically so as to scan the entire area of the inner surface of the CRT. FIG. 4 is a general perspective view of a conventional deflection yoke 1. A coil bobbin 2 is formed of a plastic material and supports associated components thereon. The coil bobbin 2 separates the horizontal coil 3 and the vertical coil 4 from each other and therefore is referred to as a separator of the deflection yoke 1.
The horizontal deflection coil 3 includes two subassemblies, each assembly being substantially in the shape of a saddle. The two subassemblies are aligned in the deflection yoke, vertically and symmetrically with respect to a horizontal axis. Likewise, the vertical deflection coil 4 includes two subassemblies, each assembly being in the shape of a saddle. The two subassemblies are aligned in a space outside of the coil bobbin 2, horizontally and symmetrically with respect to a vertical axis. A ferrite core 5 is disposed in a space outside of the vertical coil 4 so that both the horizontal coil 4 and vertical coil 3 provide magnetic deflection of the three beams with increased efficiency.
FIG. 5 is a graphical representation of the shape of the horizontal deflection coil 3. FIG. 6 is a graphical representation of the shape of the vertical deflection coil 4. The horizontal deflection coil 3 and vertical deflection coil 4 each have two assemblies of a symmetrical shape. FIGS. 5 and 6 each illustrate these two assemblies when they are assembled together. The magnetic field produced by linear portions of the respective saddle-shaped coils depicted at “A” is the major portion of the magnetic field that contributes to the magnetic deflection of electron beams. The arcuate portions in FIGS. 5 and 6 correspond to arcuate portions of FIG. 7.
A deflection yoke is required to perform two tasks: deflection of three electron-beams horizontally and vertically and convergence of the three beams on the inner surface of the screen of the color CRT. In order to achieve these tasks, the actual deflection yoke is required to generate appropriate magnetic fields, thereby necessitating complex shapes of portions depicted at “A” in FIGS. 5 and 6 which generate useful magnetic fields.
FIG. 7 illustrates an example of a deflection yoke in which actual coils are wound on the coil bobbin 2. FIG. 7 shows only an upper portion of the horizontal coil and a lower portion is omitted since the upper and lower portions are symmetrical in shape. The conductors that form the horizontal deflection coil and vertical deflection coil are of a multi-wire type in which several tens of thin wires of 0.1-0.2 mm in diameter are bundled into a single conductor having a diameter of about 1 mm.
Referring to FIG. 7, the coil bobbin 2 is formed with grooves 6 (i.e., wire channel) in the inner surface thereof, the grooves 6 accommodating the turns of horizontal coil 3 therein. Thus, properly arranging the grooves 6 allows a properly distributed magnetic field that causes the electron beams to converge on the inner surface of the panel of the CRT. When assembling the deflection yoke, the conductor needs to be turned with tension, so that the turns of conductor are accurately disposed in the grooves 6 of the coil bobbin. In practice, hook-like projections 9 and 10 are provided on the front end and rear end of the coil bobbin 2. The conductor is led out of one groove 6 with tension applied to the conductor then the conductor is turned around the hook-like projections 9 and 10 to be guided into the next groove
FIG. 8 is a cross-sectional view illustrating the positional relation among the hook-like projections 9, groove 6, and multi-wire conductor of the horizontal deflection coil 3. The conductor of the horizontal deflection coil 3 passes through an arcuate groove 7 provided at the front end of the deflection yoke, turns around the hook-like projection 9 to be redirected, and then enters the groove 6 formed in the coil bobbin 2. Several conductors of the horizontal deflection coil 3 are accommodated in the groove 7 and each of the grooves 6. The distribution of magnetic field produced by the entire horizontal coil 3 is determined by the arrangement of the groove 6 in the coil bobbin 2. It is common that the diameter of the multi-wire conductor of the horizontal coil 3 is about φ=1 mm and the width of the groove 7 is about H=5 mm. Here, when the conductor is led out of the groove 7 at the front and is bent at the hook-like projection 9 into the groove 6 formed in the coil bobbin 2, a tension force is applied to the conductor. Therefore, the turns of the horizontal coil 3 are randomly placed one after another near the hook-like projections 9. This implies that the turns of the horizontal coil are not regularly layered one after the other in the grooves 6 that play critical roles in the deflection operation of the deflection yoke and adjustment of convergence.
Recent CRTs, especially, color picture tubes for a display monitor are used to display high-resolution images that require excellent convergence performance. Convergence performance is determined by the arrangement of the turns of coil in the grooves. With the aforementioned conventional deflection yoke, there is no regularity in the turns of coil placed in the grooves. Thus, the lack of regularity inherently results in variations in convergence that is not negligible. Such a deflection yoke is not suitable for ensuring regularity of turns of coil in the grooves.
Deflection yokes have particularly stringent convergence requirements, for example in the field of a color picture tube for a display monitor. Thus, deflection yokes should have minimal variations in their deflection performance.